Abstract
The degeneration of postovulatory follicles (POFs) in time and at different temperatures was studied for the Bay of Biscay anchovy. For this purpose a key of 7 POF stages, solely defined on the basis of their histological degeneration characteristics, was applied. The novelty of this procedure is that it separates staging of POFs from their ageing process. The female gonads, taken from several captivity experiments and field samples, were classified in this way. Water temperature in captivity tanks corresponded to high values (17-21°C), except for one case in which different day and night temperatures were applied. In addition, 472 field samples (11948 anchovy females) from several cruises were examined; of these, 126 samples (3348 females) were identified as coming from areas of high sea surface temperature (weighted mean =17.76°C, s.d.=0.84) and 131 samples (3181 females) as coming from areas of low sea surface temperature (weighted mean =14.42°C, s.d.=0.75). There was close agreement in the succession of POF stages over time after spawning between the experiment and the field samples. The first four stages of POF degeneration occurred in less than 24 h, and by the end of the first day the POFs were mainly in Stage V. Stages VI and VII showed their highest occurrence during the first and second half of the second day after spawning, respectively. Full resorption of POFs was achieved in about 55-60 h. For the range of temperatures examined (13-19°C), little effect of temperature on the degeneration of POFs over time was noticed. The advanced degeneration stages were found all day round, showing some overlapping periods when successive spawning cohorts co-occurred. The application of these results for ageing POFs is discussed.
Highlights
The daily spawning fraction of fishes can be estimated using the incidence of females with postovulatory follicles (POFs) that remain within the ovaries for a certain time period after spawning, until full resorption (Hunter and Goldberg, 1980; Hunter and Macewicz, 1980; 1985)
On the basis of this work, POF degeneration levels of the northern anchovy were described and grouped into three daily levels. The description of their degeneration over time, and its correspondence with spawning cohorts in the northern anchovy, has served to guide many of the subsequent applications of the POF method for estimating the spawning frequency, with minor modifications according to specific characteristics of each population (Alheit et al, 1984; Armstrong et al, 1988; Sanz et al, 1992; Palomera and Pertierra, 1993; and Ward et al, 2001)
The objective of this study was to assess the degeneration rate of POFs until full resorption is reached within the ovaries of the European anchovy, both in captivity and in the wild and for the temperatures ranges encountered during adult sampling surveys in the Bay of Biscay
Summary
The daily spawning fraction of fishes can be estimated using the incidence of females with postovulatory follicles (POFs) that remain within the ovaries for a certain time period after spawning, until full resorption (Hunter and Goldberg, 1980; Hunter and Macewicz, 1980; 1985). On the basis of this work, POF degeneration levels of the northern anchovy were described and grouped into three daily levels The description of their degeneration over time, and its correspondence with spawning cohorts in the northern anchovy, has served to guide many of the subsequent applications of the POF method for estimating the spawning frequency, with minor modifications according to specific characteristics of each population (Alheit et al, 1984; Armstrong et al, 1988; Sanz et al, 1992; Palomera and Pertierra, 1993; and Ward et al, 2001). All these studies have revealed the ephemeral life of POFs, lasting usually between 15 to 72 h, according to species and spawning temperatures (Hunter and Macewicz, 1985; Clarke, 1987; Fitzhugh and Hettler, 1995)
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